With the advancement of technology, and the need for instantaneous information, the ability to transfer digital information from one location to another, such as from a central office (CO) to a customer premises (CP) has become more and more important. Allowing for increasing data transmission rates has, in fact, become a requirement, as opposed to an option.
In a digital subscriber line system (DSL), data is transmitted from a CO to a CP via a transmission line, such as a two-wire pair, and transmitted from the CP to the CO as well, either simultaneously or at different sessions. The same transmission line might be utilized for data transfer by both sides or the transmission to and from the CO might occur on two separate lines. The CO is basically comprised of a digital signal processor (DSP) which receives information from a data source and sends information to an analog front-end (AFE). The AFE interfaces between an analog line, such as the two-wire pair, and the DSP and functions to convert digital data, from the DSP, into a continuous time analog signal.
The analog signal is delivered, via a line driver, which is separate from the AFE, in accordance with the amount of power required to drive the amplified analog signal through the two-wire pair to the CP. A hybrid, which is located at both the CP and CO, is used to de-couple the received signal from the transmitted signal, by subtracting the transmitted signal from the sum of the transmitted and received signals. The AFE then converts the received analog signal into a digital signal, which is then transmitted to a DSP. Finally, the digital information is transmitted to the data source specified to receive such information.
As an important part of the abovementioned system responsible for proper transmission and reception of data in a broadband network, the AFE performs multiple functions in addition to converting a digital signal into a continuous time analog signal. However, the functionality of the AFE is particular to the specific DSL application considered, wherein factors such as signal bandwidth, data reach, signal quality, power budget, line power, and different applicable standards determine the optimum AFE. Unfortunately, due to the vast number of DSL applications available, including, but not limited to, HDSL, ADSL, MSDSL, 2B1Q HDSL and RADSL, it has been necessary to purchase separate individual AFEs to perform the functions necessary for each individual DSL application enumerated. Therefore, as an example, if a broadband network were to function on HDSL and ADSL applications, two separate AFEs would have to be purchased and implemented, specifically, one for HDSL applications, and one for ADSL.
Considering the many flavors of each DSL application, this problem becomes even more apparent. Limiting to only ADSL, currently there are eight main flavors on the market including DMT and CAP, light and heavy, FDM and echo canceled. For each one of these, the optimum solution is different on the CP and CO, so ideally 16 different AFEs are needed simply to cover the ADSL market. This necessity for separate AFEs has led to excessive cost in maintaining an adaptable CO or CP.